I've made this repeatedly in the past and it's always very good so decided it would be the perfect thing for lunch today.
Here's the recipe from Real Simple Magazine, if you're interested in trying it. I've made a few alterations to the recipe to suit me, but you might find it perfect the way it is.
Here are my changes... I use 15-18 shells, 1 15 oz container of Ricotta, 1 cup chopped spinach and 1/4 cup Parmesan instead of the quantities called for. I also use Classico Fire Roasted Tomato & Garlic sauce (instead of marinara) to which I add ground oregano, basil, thyme, sliced black olives and sliced artichoke hearts. I also save some of the sauce to ladle over the top of the shells after the mozzarella cheese.
Anyway, it tastes great, it's easy and there's no meat in it (which pleases me since I'm not an avid meat eater).